We observed, photographed, and recorded (video and audio) spawning of five whitefish species — Coregonus migratorius (Baikal basin), C. peled, C. tugun, C. pidschian, C. muksun (the Ob basin) — in the spawning devices. All species spawned in autumn in the dark and the spawning period lasted 10–30 days. Individual fish spawned several times during the night and the spawning behaviour consisted of three, cyclically repeated phases: courtship, mating and recovery. Spawning occurred in male–female (with males to be initiators) or male–male combination, and took place either in the water column or near the water surface. A mating act consisted of a rhythmic parallel movement of the fish swimming side by side with the synchronous release of the gametes. Three types of mating acts were observed: vertical (from bottom to top), horizontal and combined including both vertical and horizontal movements. The male in the spawning pair moved forward towards the female by the length of its head; it rhythmically struck the back of the female's abdomen by bending the caudal peduncle. Depending on the species and size of the fish, the mating act lasted for 0.3–3 s within 0.3–2 m. The frequency of rhythmic body collisions was on average 17 Hz for C. migratorius and C. pidschian, while for C. tugun and C. peled it was 25–27 Hz. An egg batch released during the mating act amounted to about 90 eggs for C. tugun and 290–370 for C. peled, which corresponded to 1%–6% of the total fecundity of a female. A female participated in 20–100 mating acts during 1–3 nights. Eggs cannibalism was also observed. During spawning, eggs were widely dispersed across the spawning area, which may be regarded as an adaptation aimed at increasing survival rate during embryogenesis.
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Vol. 58 • No. 4-6